/Engine/Plugins/Runtime/MeshModelingToolset/Source/ModelingComponents/Public/InteractiveToolActivity.h
Passing data back and forth can be done either by letting a tool activity use a specific context object that the tool can prep in the context store, or by requiring the host to implement specific interfaces (that the activity can check for inSetup()).
[UCLASS](Programming/UnrealArchitecture/Reference/Classes#classdeclaration)() class UInteractiveToolActivity : public [UInteractionMechanic](API\Runtime\InteractiveToolsFramework\UInteractionMechanic)